Production of chemicals from microorganisms has been an important application of biotechnology. Tyrosine is an attractive chemical for production in microorganisms due to its nutritional and pharmaceutical uses, such as being a dietary supplement and a reagent for production of the anti-Parkinson's drug, L-DOPA. In addition, tyrosine has potential as a reagent for the production of other chemicals with valuable industrial applications. Compounds that may potentially be made from tyrosine include (S)-4-(2-chloro-3-(4-n-dodecyloxy)-phenylpropionato)-4′4(2-methyl)butyloxy-biphenylcarboxylate (CDPMBB; Kumar and Pisipati (Z. Naturforsch. 57a:803-806 (2002)), p-hydroxycinnamic (pHCA; U.S. Pat. No. 6,368,837, US20050148054A1), p-hydroxystyrene (pHS; also know as p-vinylphenol; US2004001860), and acetylated derivatives thereof, such as p-acetoxystyrene (also known as ASM). CDPMBB is a ferroelectric material for use in ferroelectric liquid crystals (FLC). PHCA is a useful monomer for production of Liquid Crystal Polymers (LCP). LCPs may be used in electronic connectors and telecommunication and aerospace applications. LCP resistance to sterilizing radiation has also enabled these materials to be used in medical devices as well as chemical, and food packaging applications. Hydroxystyrenes have application as monomers for the production of resins, elastomers, adhesives, coatings, automotive finishes, inks and photoresists, as well as in electronic materials. They may also be used as additives in elastomer and resin formulations.
Tyrosine is made naturally in microorganisms, but is generally present at low levels that are sufficient for cellular growth. The tyrosine biosynthetic pathway branches from the phenylalanine biosynthetic pathway with the chorismate mutase/prephenate dehydrogenase enzyme, encoded by tyrA in E. coli, acting on the chorismate substrate. In the phenylalanine pathway chorismate is the substrate of chorismate mutase/prephenate dehydratase, which is encoded by the pheA gene in E. coli. 
Microorganisms with increased levels of tyrosine production have been obtained through traditional genetic methods as well as through genetic engineering. Expression of either pheA, or the genes encoding chorismate mutase/prephenate dehydratase in other organisms, has been reduced or eliminated, thereby reducing or eliminating competition for the chorismate substrate by chorismate mutase/prephenate dehydratase, resulting in increased tyrosine production [Maiti et al. (1995) Microbial production of L-tyrosine: a review. Hindustan Antibiot. Bull. 37:51-65].
Separately, either tyrA expression or the genes encoding chorismate mutase/prephenate dehydrogenase in other organisms has been increased thereby increasing the cellular capacity to direct chorismate toward tyrosine production, with increased chorismate mutase/prephenate dehydrogenase enzyme activity. EP 0332234 discloses a process for producing tyrosine in a Corynebacterium or Brevibacterium host by transforming with a plasmid carrying genes encoding 3-deoxy-2-keto-D-arabino-heptulosonate-7phosphate (DAHP) synthase (first enzyme of the aromatic amino acid biosynthetic pathway), chorismate mutase, and prephenate dehydrogenase. EP 0263515 discloses a process for producing tyrosine in a Corynebacterium or Brevibacterium host that produces tryptophan. The tryptophan producing Corynebacterium or Brevibacterium host is transformed with a plasmid carrying genes encoding DAHP synthase and chorismate mutase.
Commonly owned US20040248267 discloses engineering of a tyrosine excreting E. coli strain by first introducing a mutant pheA gene. Then in a second separate step, a trc promoter driven tyrA gene was introduced. Rare transductants having both introductions were identified as tyrosine excreting strains.
In addition, commonly owned US 20050148054 A1 discloses increasing tyrosine production by expressing phenylalanine hydroxylase in a recombinant organism to convert phenylalanine to tyrosine.
In spite of the efforts to engineer microorganisms for the production of tyrosine the highest reported level is only 26 g/l for Corynebacterium glutamicum (Ikeda, M. and R. Katsumata. 1992. Appl. Environ. Microbiol. 58: 781-785). There remains a need therefore for microorganisms that produce L-tyrosine in higher levels to facilitate the commercial production of tyrosine. Applicants have solved the stated problem by engineering a recombinant enteric bacteria to produces L-tyrosine at levels in excess of 26 g/l.